1. Field of the Invention
The present invention relates to apparatuses, methods and computer program product that involve color space conversion processing on image data. More particularly, the present invention relates to apparatuses, methods and computer program product used in, and by, devices such as digital still cameras (DSC), digital video cameras (DVC), scanners, which capture and store images in a first color space, with a recognition that a color space conversion operation will be performed in downstream processing. The invention also relates to the apparatuses, methods and computer program product that perform the downstream processing, perhaps in the output device, such as a printer or display. Thus, the invention also relates to signal processing hardware and software components, including propagated data signals, and presentation devices, such as printers.
2. Discussion of the Background
In recent years there has been growing demand for DSCs, DVCs, scanners, and other devices that handle digital photographic or scanned images in the form of easily manipulated image files. In DSCs and similar devices, digital photographic image data is typically stored in JPEG format files, one of the formats used for compressed image files. In JPEG files, image data is defined using a YCbCr color space so as to enable a high compression ratio. Accordingly, devices such as DSCs translate photographic image data represented in an RGB color space to a YCbCr color space. The RGB color space used by devices such as DSCs is typically a standard color space for personal computer CRT monitors (e.g., sRGB: IEC61966 2-1).
Since personal computers use an RGB color space as the standard color space for image data, a personal computer receiving a JPEG file must decompress the JPEG file and convert the color space of the image data from a YCbCr color space to an RGB color space. Image data that has been converted to an RGB color space is either displayed on a monitor, or is converted to a CMYK color space for print output on a print medium via a printer.
Conventional image processing by personal computers is typically based on an assumption that images will be output on a CRT monitor, so the color space of image data that has been converted from a YCbCr color space to an RGB color space is typically “clipped” during conversion to the sRGB color space, which has color space characteristics adapted to display on CRT monitors, and is standard across personal computers.
Thus, when a JPEG file generated by an image data generating device such as a DSC is decompressed and converted from a YCbCr color space to an RGB color space by a personal computer, color values outside the gamut of the sRGB color space are inevitably rounded, even in cases where the gamut of the RGB color space of the image data exceeds the gamut of the sRGB color space. In such cases, colors that exceed the gamut of the sRGB color space are not reflected in the output image. As a result, the full color reproduction capabilities of an output device is not utilized—even where the reproducible color range of the output device exceeds that of the sRGB color space. Another drawback is a failure to effectively utilize the full color reproduction capabilities of DSCs.
The sRGB color space, which is matched to the color reproduction capabilities of monitors, has been widely adopted as the standard RGB color space, and conventional YCbCr-to-RGB color space conversion currently relies on conversion matrices that have been designed on the assumption that images will be displayed on a monitor. Thus, even if one were to define a new RGB color space having a wider gamut than the sRGB color space, unless one also adopted the new RGB color space as the color space used by all the devices—from the input device to the output device—for image processing, the lack of a common standard would result in an inability to easy modify color space attributes.
Some image file users overcome this problem by performing image file image adjustment using image file correction software that gives output accurately reflecting the native color space of a DSC or other device. However, such image adjustment is rather complicated.
With the foregoing in view, it is an object of the present invention to provide an image output device capable of accurately outputting information indicating the color space used when image data is generated. It is a further object to provide an image output device capable of effectively utilizing the color reproduction range of a device that generates image data, or of a device that outputs image data.